BBC Vigil fans became “distracted” as DCI Amy Silva had some racy flashbacks while struggling for air in a torpedo tube.
Amy, who is played by Suranne Jones, glanced back at the moment she lay in bed naked with Kirsten Longacre.
It seemed that the pair had enjoyed a moment of passion together before Amy rolled over showing naked back.
At which point, Kirsten uses her hand to tap out morse code onto Amy’s bare flesh , spelling out “I love you”.
As her life flashed before her, Amy remembered the moment she’d let Kirsten down as she could not say the words she’d expressed on her back.
In spite of the dramatic scenes – including a brutal stabbing – some fans were more taken back by the romance on screens.
One person wrote: “Kirsten telling Amy she loves her #vigil The flashbacks are KILLING ME #Vigil.”
Another tweet read: “I know I am late to the party but the ‘I like you’ scene with Suranne Jones and Rose Leslie at the end of Episode 4, was some high-end romance s**t right there.”
A third exclaimed: “Chemistry off the charts, line deliveries also pitch perfect. #Vigil.”
A fourth remarked: “Oh, these lesbian flaskbacks are everything #vigil.”
While a fifth said: “Again and again the morse code that Kirsten taught Amy is saving her life and I love that #vigil.”
As the finale came to a close, Amy and Kirsten were reunited in an emotional scene.
Having been trapped in a torpedo tube, DCI Silva had regretted not telling Kirsten her true feelings.
Kirsten wanted reassurance that Amy wouldn’t go back to her old ways, asking: “How do I know you won’t go back to where you were before?”
“When I was trapped all I could think about was you,” explained Amy in the emotional scene.
Meanwhile, the biggest shock came mid episode, when DCI Silva was freed from the torpedo tube by Lt Cdr Mark Prentice.
After rescuing DCI Silva, he was savagely stabbed to death by the Russian double agent on board, CPO Matthew Doward (Lorne MacFadyen).